Maintain groups when importing svg files

[henrikmidtiby]

Overview: What does this pull request change?

This is a work in progress for being able to access groups in objects created from SVG files.
I hope that this could be useful for addressing the following issues and pull requests:

• Select SVG shapes by id #3941
  • This issue should be fixed by the suggested PR directly
• Fix #3548: Match MathTex subscripts/superscripts by position #4457
  • This PR can be improved by the suggested PR
• Rendered submobjects of MathTex may not correspond to their tex strings #3548
  • This issue can be solved by building on top of the suggested PR
• TeX splitting can cause the last parts of an equation to not be displayed #2970
  • This issue is solved by the suggested PR.
• Tex splitting issue with \frac numerator #2884
  • I think that this issue can be handled better based on the suggested PR

When reading data from a SVG file, maintain the groupings of the document, which also allows the user to select (groups of) elements by their id.

Motivation and Explanation: Why and how do your changes improve the library?

Links to added or changed documentation pages

Further Information and Comments

The following example demonstrates how custom grouping of elements inside a latex equation can be achieved. This is based on an idea presented by @behackl in the discord dev-chat the 18th of august 2025.

from manim import *

class SvgTest3(Scene):
    def construct(self):
        t = MathTex(r'\frac{a}{b \special{dvisvgm:raw <g id="unique02">}\cdot c \special{dvisvgm:raw </g>}}')
        t.set_color(WHITE)
        t.id_to_vgroup_dict['unique02'].set_color(RED)
        self.add(t)

renders like

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested